Remote-processing RPC-330 Manuel d'utilisateur télécharger pdf (Page 36)

ANALOG INPUT SECTION 10

Page 10-2 RPC-330

When channel = even

Pol. + - + - + - + -

CH # 0 1 2 3 4 5 6 7

channel 0 2 4 6

When range = 0, the input is ±2.5 volts and a 1 = 0 to

5 volts.

Differential Mode

When differential m ode is specified, inputs are actually

pseudo-differential. What this means is that a ground

reference is needed. For example, you cannot place a

battery between channel 0 and 1 and get an accurate

reading. The (-) input must be referenced to ground.

An example of where pseudo-differential works is an

output from a bridge network.

A pseudo-differential input subtracts the DC component

from an input. The IC maker recommends the (-) input

remain stable within 1 count with respect to ground for

best results. Connecting a 0.1 uF capacitor from the (-)

input to ground works well.

When operating in differential mode, relative + and -

voltages must be connected to specific inputs. When

inputs are reversed, a conversion returns a 0. When the

relative voltage changes, perform a conversion on the

alternate channel. CONFIG AIN must be perfor med on

both channels to be valid.

Pairs of channels can be differ ential while others single

ended. Thus, if channel 0 and 1 are differ ential inputs,

channels 2-7 may be single ended.

Examples u sing CON FIG AIN

Below are sample syntaxes for CONFIG AIN

Differential, 0 to + 5V input

CONFIG AIN 0,0, 1

CONFIG AIN 1,0, 1

Perform a conversion as normal:

A = AIN(0)

The difference between channel 0 and 1 is returned.

When channel 1 is more positive than channel 0, the

result is zer o. T he difference can be read on channel 1

by performing:

A = AIN(1)

Single-ended, ±2.5V input

CONFIG AIN channel,1,0

The result is 0 for -2.500V input, 2048 for 0.000V, and

4095 for + 2.4988V.

Acquiring Analog Data

Analog data is accessed with the AIN function. The

syntax is:

A = AIN(channel)

This function assigns the analog value of a channel to the

variable; A in this case. The value returned is alway s in

the 0 to 4095 range because the converter is 12 bits.

Power up or reset default configures inputs to the 0-5V

range, single ended.

To view the result of a conversion in the command

mode, type:

print ain(0)

The result at channel 0 is returned. The returned value

will always be in the 0 to 4095 range. When using a

channel in the ±2. 5V ra nge, the value returned is

interpreted differently. Zero count is now -2.500V,

4095 is + 4.9988, and 2048 is 0.000V.

Use the following formulas to convert a returned number

to a voltage:

0 - 5V A = .001221 * AIN(channel)

±2.5V A = .001221 * ain(channel) - 2.5

The AIN function requires about 1.5 ms to convert the

data. Additional time is needed to store the data. The

example below takes 255 data samples and stores them

into an array which requires 6 bytes per entry. The

second example takes only two byes per entry, can save

to extended m emor y, but requir es a longer time to get a

data point.

The program below takes about 1. 5 ms per data point.

10 DIM A(254)

20 FOR X=0 TO 254

30 A(X) = AIN(0)

1 2 ... 31 32 33 34 35 36 37 38 39 40 41 ... 47 48

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Remote-processing RPC-330 Manuel d'utilisateur Page 36

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